Many modem aircraft are equipped with an airborne auxiliary power unit (“APU”) that provides electrical and pneumatic power to various parts of the aircraft. Typically, APUs include mounts, inlet and exhaust, and pneumatic (bleed) and fire containment systems, including systems for detecting and extinguishing fires. FIG. 1 shows a typical APU 100 installed in the tailcone of an aircraft (shown in dashed outline 105). Some of the systems that support the APU 100 include an inlet system 110, a mount system 115, a pneumatic system 120, and an exhaust system 125. The APU exhaust system 125 may perform various functions, including evacuating APU exhaust gas from the aircraft, attenuating exhaust noise, and providing cooling airflow for the aircraft APU compartment when used in conjunction with an eductor system.
To attenuate exhaust noise, the exhaust system 125 may include a muffler section, such as muffler section 130, shown in FIG. 2, which includes an outer can 135 that houses an acoustic liner 140 and a series of baffles 145. Forward 150 and aft 155 end caps terminate the muffler section 130 and are typically attached to components of an eductor system (such as a bellmouth or primary pipe) and to a portion of an axially extending exhaust piping 160.
During aircraft operation, the APU exhaust system 125 is typically exposed to relatively high temperatures, for example, temperatures greater than about 1,000° F. Accordingly, the muffler section 130 is typically fabricated from high temperature steels, such as stainless steel or inconel, and may be externally covered with a thermal blanket 165, as shown in FIG. 2. However, high temperature steels have relatively high densities and thermal blankets are relatively heavy. Consequently, undesirable weight may be potentially added to the aircraft.
Accordingly, there is a need for reducing the weight of the mufflers used in aircrafts equipped with airborne APUs. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background